This invention relates to methods for fabricating polymeric articles, including multiple layer film, sheet materials, and packages.
As used herein, "structure" means and includes multiple layer film and packages made with the multiple layer films of the invention.
Vinylidene chloride copolymers (VDC) provide barrier to transmission of moisture vapor and oxygen, and therefore are desirable for use when those properties are important. It is commonly known that the extrusion of VDC copolymers is accompanied by a plurality of processing problems. These processing problems generally relate to the sensitivity of VDC copolymer to the combination of high temperature contact between the VDC and hot metal, and especially the amount of time for which high temperature contact is maintained during the extrusion process.
The apparatus and processes disclosed in application Ser. No. 204,485 now abandoned provide for the encapsulation of a sensitive core layer. This provides protection for the core layer (e.g. VDC copolymer), effective to attenuate the problem of VDC copolymer degradation, in the multiple layer film so produced. But the edge portions of the films are devoid of core layer. That is, the edges of the encapsulated layer do not extend into the normal edge portions of the film (e.g. about 1-2 inches on each side) which are typically trimmed off of a cast extruded film, extruded from a slot die. So the trim cutters must be set inwardly from the extruded edge of the film, further than normal, to ensure that the trimmed edges include the core layer. As a result, there is more than the usual amount of waste edge trim.
The core layer can be extended to within normal trim width, by reducing the flow rate of the encapsulating layer. However, if this is done, the encapsulating layer does not assuredly protect the opposing non-edge/elongate surfaces of the sensitive core layer in the slot die, although the core layer may still be protected in the transport pipe and in a feedblock between the encapsulator and the die.
It is an object of this invention to provide novel articles and processes, with the versatility of being able to control and position the location of the edge of an encapsulated core layer, preferably of heat sensitive material, relative to the outer edge of the sheet, while independently controlling the thickness of covering polymer materials on the opposing surfaces of the encapsulated layer.
It is a further object of this invention to achieve the preceding objective by coordinating the flow rate of an additional melt stream, from an additional extruder, with the flow rate of the encapsulating melt stream.
It is another object to reduce, or otherwise control, the edge trim of a coextruded film comprising a layer of a VDC copolymer.
It is still another object to accomplish the control of the edge trim and coordination of the flow rates while reducing the need for use of more costly specialized polymer compositions.